Under the old, manual method of tube bending, a tube was advanced manually through a fixed die and a manual die one small increment at a time, and the movable die was pivoted so as to bend the tube to the desired curvature. Such a process was obviously time-consuming and difficult to carry out precisely. New, automatic bending machines, called multi-axis benders, speed the tube bending process and its precision by forcing the tube continuously through the fixed and movable dies, with the movable die being preprogrammed to swing in a pattern that will continuously bend the tube into the desired shape. A great deal of axial pushing force has to be applied to the tube as it is fed through the dies, and it has to be supported along its length as this force is applied. Typically, the tube is encased in a close fitting channel as it moves, to keep it from buckling. A pusher apparatus is driven forcefully by some drive mechanism, such as a ball screw machine, along the same channel, to push the tube though the channel. Some part of the pusher apparatus extends out to the side of the channel, through a slit or the like, so that it can be moved along by the drive mechanism.
Some part of the pusher apparatus has to directly, physically engage the tube as it is pushed through the channel. This structure will have to fit inside the same channel as the tube it is pushing, and so, ideally, will have the same shape as the tube. Most conveniently, a piece of tube just like the tube being bent would be used. However, there is nothing to keep the pusher tube from collapsing inside of the pushed tube, especially under the high forces involved. As well as the need to support the outside of the tube as it is forced through the channel, there is a need to maintain the inside of the tube against collapse as it is bent by the dies. Flexible mandrels exist that make a close, slip fit inside that section of the tube that is being continuously bent, which is that part of the tube that is located between the fixed and movable dies. It is necessary to somehow insert and withdraw these mandrels into and from the tubes, and to keep them located between the fixed and movable dies as the tube is being pushed through the dies.